%% A remote spawns an Erlang port running the 'remote' program from
%% p11-kit.

%% Receive p11 requests from p11p_server, forward them to the remote,
%% wait for a reply. If a reply is received within a timeout period,
%% forward the reply to the requesting p11p_server. If the request
%% times out, inform the remote manager (our parent).

%% TODO: "remote" is not a great name and we shouldn't just inherit it
%% from p11p-kit

-module(p11p_remote).
-behaviour(gen_server).

%% API.
-export([start_link/3]).
-export([request/2, add_to_outbuf/2, stop/2]).

-include("p11p_rpc.hrl").

%% Genserver callbacks.
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
         code_change/3]).

%% Records and types.
-record(state, {
	  port :: port(),
	  replyto :: pid() | undefined,
	  timer :: reference() | undefined,
	  token :: string(),			% Name
	  outbuf = <<>> :: binary(),
	  msg :: p11rpc:msg() | undefined
	 }).

%% FIXME: move to config
-define(P11KITREMOTE_PATH, "/home/linus/usr/libexec/p11-kit/p11-kit-remote").

%% API.
-spec start_link(atom(), string(), string()) -> {ok, pid()} | {error, term()}.
start_link(ServName, TokName, ModPath) ->
    lager:info("~p: p11p_remote starting for ~s", [ServName, ModPath]),
    gen_server:start_link({local, ServName}, ?MODULE, [TokName, ModPath], []).

-spec request(pid(), p11rpc_msg()) -> ok.
request(Remote, Request) ->
    gen_server:call(Remote, {request, Request}).

add_to_outbuf(Remote, Data) ->
    gen_server:call(Remote, {add_to_outbuf, Data}).

%% Use stop/1 instead of gen_server:stop/1 if you're uncertain whether
%% Pid is alive or not. An example of when that can happen is when the
%% manager receiving a server_event about a lost client. If the server
%% process terminated on request from a remote which has timed out on
%% an rpc call, chances are that the remote has already terminated by
%% the time the manager is to act on the lost client.
stop(Pid, Reason) ->
    gen_server:cast(Pid, {stop, Reason}).

%% Genserver callbacks.
init([TokName, ModPath]) ->
    Port = open_port({spawn_executable, ?P11KITREMOTE_PATH},
		     [stream, exit_status, {args, [ModPath, "-v"]}]),
    lager:debug("~p: ~s: new remote port: ~p", [self(), ?P11KITREMOTE_PATH, Port]),
    {ok, #state{port = Port, token = TokName}}.

handle_call({add_to_outbuf,  Data}, _From, State) ->
    {reply, ok, do_add_to_outbuf(Data, State)};
handle_call({request, Request}, {FromPid, _Tag}, #state{port = Port} = State) ->
    %%lager:debug("~p: sending request from ~p to remote ~p", [self(), FromPid, Port]),
    NewState = do_send(do_add_to_outbuf(p11p_rpc:serialise(Request), State)),
    {reply, ok, NewState#state{replyto = FromPid, timer = start_timer(Port)}};
handle_call(Request, _From, State) ->
    lager:debug("~p: Unhandled call: ~p~n", [self(), Request]),
    {reply, unhandled, State}.

handle_cast({stop, Reason}, State) ->
    {stop, Reason, State};
handle_cast(Cast, State) ->
    lager:debug("~p: unhandled cast: ~p~n", [self(), Cast]),
    {noreply, State}.

%% TODO: dedup code w/ p11p_server
handle_info({Port, {data, Data}}, #state{replyto = Pid} = State) when Port == State#state.port, State#state.msg == undefined ->
    Version = hd(Data),			     % First octet is version.
    {ok, _BytesAdded} = p11p_server:add_to_clientbuf(Pid, <<Version>>),
    {noreply, handle_remote_data(State, p11p_rpc:new(), tl(Data))};
handle_info({Port, {data, Data}}, #state{msg = Msg} = State) when Port == State#state.port ->
    {noreply, handle_remote_data(State, Msg, Data)};
handle_info({timeout, Timer, Port}, #state{token = TokName, replyto = Server} = State) when Port == State#state.port, Timer == State#state.timer ->
    lager:info("~p: rpc request timed out, exiting", [self()]),
    p11p_remote_manager:server_event(timeout, [TokName, Server]),
    NewState = State#state{timer = undefined},
    {stop, normal, NewState};
handle_info(Info, State) ->
    lager:debug("~p: Unhandled info: ~p~n", [self(), Info]),
    {noreply, State}.

terminate(Reason, #state{port = Port}) ->
    lager:debug("~p: remote terminating with reason ~p", [self(), Reason]),
    port_close(Port),
    ok.

code_change(_OldVersion, State, _Extra) ->
    {ok, State}.

%% Private
do_add_to_outbuf(Data, #state{outbuf = Buf} = State) ->
    %%lager:debug("~p: adding ~B octets to outbuf", [self(), size(Data)]),
    NewBuf = <<Buf/binary, Data/binary>>,
    State#state{outbuf = NewBuf}.

do_send(#state{port = Port, outbuf = Buf} = State) ->
    %%lager:debug("~p: sending ~B octets to remote", [self(), size(Buf)]),
    port_command(Port, Buf),
    State#state{outbuf = <<>>}.

handle_remote_data(#state{replyto = Pid, timer = Timer} = State, Msg, Data) ->
    case p11p_rpc:parse(Msg, list_to_binary(Data)) of
	{done, NewMsg} ->
	    cancel_timer(Timer),
	    {ok, _BytesSent} = p11p_server:reply(Pid, NewMsg),
	    State#state{msg = p11p_rpc:new(NewMsg#p11rpc_msg.buffer)};
	{needmore, NewMsg} ->
	    State#state{msg = NewMsg}
    end.

start_timer(Port) ->
    %%lager:debug("~p: starting timer", [self()]),
    erlang:start_timer(3000, self(), Port).

cancel_timer(Timer) ->
    %%lager:debug("~p: canceling timer", [self()]),
    erlang:cancel_timer(Timer, [{async, true}, {info, false}]).